This invention relates to a true two-stroke (power and exhaust) internal combustion piston engine combining direct injection of all combustion and working elements with exhaust valve(s) that open early during the power stroke if cylinder pressure falls below exhaust manifold pressure.
With the exception of certain engines designed for applications where ambient atmosphere is not available (such as submerged submarines), all internal combustion engines in wide use rely on ambient atmosphere to provide both the oxidizer and primary working fluid for converting heat of combustion to mechanical force. Even engines used in submerged submarines use the same cycle and dynamics as conventional engines with added components/controls to replace the ambient atmosphere that is not available (compressed air tanks or oxygen plus inert gas).
The power and efficiency of conventional internal combustion engines is largely a function of how much ambient air can be compressed into a cylinder to react with the appropriate amount of fuel. Thus large amounts of power can be generated using a large-displacement, normally aspirated engine or a much smaller displacement engine with additional components and systems to maximize the air forced into the cylinder(s). As ambient air is used, all the mechanical/other methods to place the air into the cylinder and compress the air must be on the vehicle and some amount of the mechanical force from the engine must be used to compress the air drawn into the engine.
Because the same cylinder is used to take in the ambient air and compress it to efficient pressure, the effective displacement is the total displacement of the piston travel. The most efficient operating region is near full power, and thus the required displacement of a given engine/vehicle combination is often determined by the maximum power desired even though the maximum power is seldom used or efficient in normal use.
The use of ambient air is the source of many other problems confronting conventional internal combustion engine designers. Ambient air consists largely of nitrogen and oxygen but may also contain any number of local variations from humidity to pollutants. Nitrogen limits the thermodynamic efficiency of the engine because it limits the temperature of combustion to control undesirable nitrogen-oxygen compounds in exhaust products. These and other undesirable byproducts require exhaust catalysts to remove or change the exhaust before it is vented into the atmosphere.
Great strides have been made in the design of modern internal combustion engines to address the efficiency and maintain clean operating characteristics but the limits to using ambient atmosphere as oxidizer/working fluid are close. A step beyond will be required to reach the next level of advancement.
In the 1970s several patents suggested using non-atmospheric oxidizers with otherwise conventional engines as a method of addressing atmospheric pollution. These patents included suggestions of the possibility of a two-stroke engine implemented in this manner with conventional intake and exhaust valve operation. No commercial product appears to have resulted from these inventions.